The present invention relates to a towing device for selectively locking a towing load.
A towing tractor generally includes one of towing devices. Referring to FIGS. 8 through 10, a towing device of a towing tractor generally has a support member 3, a shaft C, a first link member 5, a second link member 15, an operational member 6, a drawbar pin 16 and a drawbar bracket 17. The support member 3 is erected near the rear side of a vehicle body 2 and pivotably supports the shaft C. The proximal end of the first link member 5 and the proximal end of the operational member 6 are fixedly connected to the shaft C so that the shaft C, the first link member 5 and the operational member 6 integrally pivot. The second link member 15 is pivotably coupled to the distal end of the first link member 5 at its one end and is also pivotably coupled to a head 16a of the drawbar pin 16 at the other end. The drawbar bracket 17 is fixedly connected to the rear end and lower side of the vehicle body 2. The drawbar pin 16 is fitted in the drawbar bracket 17 to be raised or lowered. The drawbar pin 16 is coupled with a drawbar of a carriage so that the carriage is towed. The first and second link members 5 and 15 constitute a link mechanism.
A stopper or a rotation regulating member includes a stopper bracket 10 and a stopper bolt 11. The stopper bracket 10 is fixedly connected to the support member 3. The stopper bolt 11 is fitted into a through hole of the stopper bracket 10 and is adjustable in its level to regulate the maximum upward rotational distance of the first link member 5. The stopper bolt 11 is supported by the stopper bracket 10 and is located under the operational member 6 so as to correspond with the rotational range of the operational member 6. The stopper bolt 11 contacts the operational member 6 as the drawbar pin 16 is raised upward through the link mechanism.
A clevis 7 is coupled to the distal end of the operational member 6 at its one end and is connected to a cable 8 at the other end. The cable 8 travels near a rear axle of the vehicle body 2 and is ultimately coupled to a link lever 13 of a drawbar operation lever 14 that is located near an operator seat through a clevis 12. When the drawbar operation lever 14 is manipulated to raise the drawbar pin 16, the cable 8 is tensioned to pull the clevis 7 so that the clevis 7 pivots about a pivotal point between the clevis 7 and the operational member 6. As a result, the clevis 7 does not contact the stopper bracket 10.
When an operator holds a grip portion 5a of the first link member 5 and manually lifts up the first link member 5 to raise the drawbar pin 16, since the operation lever 14 is not manipulated, the cable 8 is not tensioned. Only the operational member 6 pivots about the shaft C in the counterclockwise direction in the drawings. Then, the operational member 6 pushes the cable 8 downward to bend the cable 8 so that the clevis 7 tends to pivot toward the stopper bracket 10 and the stopper bolt 11. In this case, since the length of the clevis 7 is shorter than the distance between the operational member 6 and the stopper bolt 10, the clevis 7 gets entangled with the stopper bolt 11 or the stopper bracket 10 so that a contact surface 6a of the operational member 6 does not move to contact the upper end surface of the stopper bolt 11. As a result, the drawbar pin 16 cannot completely be raised, and the manually raising operation is interrupted. The clevis 7 needs to be moved in the operator's hand to remove interference between the clevis 7 and the stopper bracket 10 and between the clevis 7 and the stopper bolt 11. Thus, the operation is complicated. Therefore, it is desired that a towing device that does not interrupt the drawbar operation by overcoming the interference between the clevis 7 and the stopper bracket 10 and between the clevis 7 and the stopper bolt 11.